In airbag modules the airbags are arranged in a folded state in their rest position in the area of a gas generator. For this it is necessary inter alia to arrange the folding and positioning in the area of the gas generator so that after the gas generator is detonated the airbag unfolds easily unhindered and can be rapidly filled with gas.
The so-called continuous fan-fold method of folding is already known. Here the spread-out airbag is placed concertina-like in folds starting from a central (imaginary) centre line and extending each side of this line so that an oblong roughly rectangular strip is produced. Then this strip itself is folded several times in its longitudinal direction by placing the ends over the middle area or by rolling in the ends. An example is shown in EP 0 614 786 A1.
The drawback with this type of folding is that after detonation of the gas generator and with the gas pressure which thereby arises in the centre of the airbag the outer folds which have been formed by cross-folding hinder the unfolding of the longitudinal folds and at first the cross folds which have been turned in last and whose outer areas can only be reached with difficulty at first by the gas pressure arising in the centre have to unfold first before the longitudinal folds which were the first to be folded when collapsing the airbag can themselves be unfolded.
Furthermore there is the drawback that the airbags folded in this way have still to be folded by hand at least in part.
From DE 41 38 645 A1 an airbag is known which is first folded in zig-zag fashion into a number of longitudinally aligned folding paths on opposite side areas of the airbag. The airbag is then folded in zig-zag fashion into a number of transversely-aligned folding paths from the rear end of the airbag outside of the socket area towards the front end of the airbag.
Furthermore an airbag is known from DE 43 43 026 A1 which is first turned in to the inside from the sides. The centers of the turned-in parts are then drawn to the outside. The airbag prefolded in this way is again folded cross-wise to the first folding direction.
Even with these types of folding there is the disadvantage that the airbags can only be mechanically folded at extremely high cost and that the folds intersect so that they impede each other as they unfold.
It is also known from DE 44 22 276 A1 to fold the airbag along main fold lines which run at least in part along closed paths round an imaginary centre on the substantially empty spread-out airbag. Thus starting from an imaginary centre of the spread-out airbag a type of concentric zig-zag or concertina-type folding is produced. The main fold lines preferably form concentric circles or ellipses.
With the airbag folded in this way, folding individual sections of the airbag over each other is no longer necessary. Furthermore by gathering up the airbag it is possible to collapse the airbag into a compact unit. The airbag folded in this way can then unfold quickly and unhindered in all directions once the gas generator is detonated and folding can also be carried out substantially automatically.